The prevention of cardiac arrhythmias such as fibrillation has long been of interest in the art. Certain cardiac stimulation circuits have been developed to produce cardiac stimulation signals to prevent or stop fibrillation. One such device is disclosed in U.S. Pat. No. 3,937,226, issued to Dr. Herman D. Funke. In the Funke device, a plurality of electrodes are connected to a heart in spaced relation to each other for sensing depolarizations that occur at a plurality of areas of the heart. Output circuitry responsive to any sensed depolarization applies stimulation signals simultaneously to a plurality of areas of the heart rapidly after sensing a depolarization. The circuitry disclosed in the Funke patent includes a free running or astable multivibrator which generates a stimulation pulse to be applied to the plurality of areas of the heart if no depolarization signal is sensed within a predetermined time period. Thus, the Funke device acts to prevent premature ventricular contractions leading to ventricular fibrillation and has the capability to operate in a demand mode in the event of bradycardia or "skipped" beats, for example.
The circuitry of the Funke patent applies a stimulation signal to a plurality of areas on the heart each time the heart beats, even when the heart is beating at a normal rate. Consequently, a considerable amount of electrical power is used by the Funke device to stimulate the heart. Since the life of an implanted cardiac stimulation device is often dependent on the life of the power supply, it is considered highly desirable to reduce the drain on the power supply whenever possible.